Electronic mail, or e-mail is a messaging service, which allows quick and economical communication in electronic form. Using the Internet, e-mail messages can be sent all over the world, in many cases practically free of charge. Furthermore, the same e-mail message can be sent to a plurality of recipients. This technique is called multicasting. As the relaying of e-mail messages is entirely automated, the e-mail messages can arrive very shortly after they are sent. E-mail messages can carry computer files such as documents, program files, and different media files like audio- or video clips.
Ordinary home users having Personal Computers (PCs) prefer not to have a permanent connection to their e-mail system (for example to the Internet) but rather to set up a temporary and remote connection to an e-mail server that stores messages received since a previous e-mail message reading session. Using this kind of connection and an e-mail message reading program, new e-mail messages can be transferred from the e-mail server to the memory or a hard disk of a PC and then be read either while the connection is still extant, or alternatively after the connection has been closed. The transmission of data between the PC and the e-mail server is typically carried out using a modem attached to the PC.
In the following, the term “sender” refers to a device that sends data intended for a receiver and “receiver” refers to a device that receives the data and to which the data was intended.
FIG. 1 shows a schematic diagram of an Internet-based e-mail system 10 comprising a sender 11, a receiver 15 and the Internet 12 having a sender's e-mail server 13 and a receiver's e-mail server 14.
In the Internet, e-mail messages are sent using certain well-known protocols. Simply speaking, an e-mail message, once composed, is packaged into a single unit, stamped with an address of the receiver and is sent to the sender's e-mail server. The sender's e-mail server forwards the message through the Internet to the receiver's e-mail server. The next time the receiver forms a connection to the receiver's e-mail server via the Internet and checks whether new e-mail messages have been received using an e-mail reading program, the receiver can download any newly received e-mail message over the connection (e.g. modem link). When the e-mail message has been received completely, it can be presented to the user. It should be noted that during the various stages of its transmission, the e-mail message is typically split into numerous smaller packets according to the data transfer protocol(s) used. On reception, the receiver gathers together all of the packets, assembles them into the correct order (if necessary) and reconstructs the e-mail message into its original form, before presenting the e-mail message to a user of the receiver.
An e-mail transmission system described above is convenient and provides the possibility for multicasting, but it is best suited, and originally intended, for receiving e-mail messages and then presenting them at the convenience of the user. Thus, the content of a given e-mail message can only be accessed after completion of the e-mail message transmission to the receiver. This is not a real problem with plain text form e-mail messages, but in the case of a large media or multimedia content (clip) it is a drawback that the user of the receiver cannot start presentation of the clip while it is still being downloaded. Another drawback is that in order to receive an e-mail message, the receiver must have a sufficiently large memory to accommodate the entire message. Particularly in mobile communications networks, or any other network in which part of the communications link is formed by a radio connection, it is also problematic to receive a long e-mail message without interruptions or errors, for example due to a temporary loss of or deterioration in radio coverage. Mobile terminals also tend to have limited memory available for the storage of received e-mail messages, which further exacerbates the problem associated with the accommodation of messages in the receiver. These problems are at least partly mitigated by the Multimedia Messaging Service (MMS).
The MMS is a new end-to-end messaging approach for one-way transmission of multimedia messages having text and/or multimedia content. MMS provides the possibility of sending multimedia messages between mobile users and between a mobile user and the Internet. There is already an agreed solution for implementation of MMS in 3rd Generation mobile communication networks. The currently specified features of the proposed MMS are described in 3rd Generation Partnership Project (3GPP) technical specification 23.140 V.3.0.1. “Multimedia Messaging Service (MMS), Functional Description, Stage 2 (Release 1999)”. The MMS proposed in 3GPP 23.140 employs a store-and-forward approach to multimedia message delivery. Multimedia messages are constructed in such a way that the media content, information necessary to describe the media content and addressing information, identifying the intended receiver of the multimedia message, are encapsulated together. The multimedia message is then sent to an MMS Centre MMSC, which in turn notifies the receiver about the multimedia message. The multimedia message is downloaded by the receiving terminal as a whole and only presented to the user once downloaded and stored in the receiving terminal.
It should be appreciated that although the term “multimedia message” is used generally to describe a message that contains more than one type of content, in this application, the term extends to cover messages that contain only one media type.
As currently specified, the MMS has a drawback: the receiving terminal must store the multimedia message before it can be presented to the user. Therefore the size of the memory of the receiving terminal sets an upper limit on the size of multimedia messages that can be downloaded. WO 99/166746 solves this problem by dividing a message into sub-messages (segments) if the entire message would not fit into the memory of the receiving terminal. These sub-messages are small enough so that the receiving terminal can individually download each of them as a whole. In that case, the receiving terminal initially downloads a first sub-message. After the first sub-message has been fully downloaded, the receiving terminal can present it. After presentation of the first sub-message, the receiving terminal can download a second sub-message and then present it. Each sub-message is downloaded and then presented by itself. The size of the sub-messages depends on the memory size of the receiving terminal and must be small enough to fit into the memory.
Apart from MMS, there are streaming-techniques used in the Internet for transmission over fixed lines. “Streaming” is a term used generally to describe the presentation of a media stream, for example an audio or video stream, or a combination of different streams, in a continuous way while this stream or those streams are being transmitted to a client over a data network. A “stream” is a flow of data typically enabling the receiver to present some continuous data such as a motion picture, voice or music. In a typical video stream, some 10 to 20 video frames are transmitted per second. In practice, streaming can be either live (real-time) or performed in an on-demand fashion. As its name suggests, “live streaming” describes the creation of a media stream from a live source, for example a stream of digital images produced by a video camera, while “on-demand streaming” describes the creation of a media stream from, for example, a file stored on a server. Streaming also involves establishing a streaming session, during which the stream or streams is or are transmitted to the client.
Within streaming there are two very important functionalities, namely streaming control and media transport. Streaming control takes care of establishing, managing and terminating a streaming session using a negotiated or pre-configured set of parameter values. Media transport concerns the transportation of media during the established session using an agreed or negotiated transport protocol. For example, there are widely agreed protocols in the Internet to provide both streaming control and media transport functionalities and these can be used as transport protocols in streaming applications.
Whilst streaming is widely used in the Internet, it has still to be adapted for use in mobile communication networks. It should be appreciated that the use of streaming is desirable in mobile networks, since mobile terminals typically have limited storage capacity (memory). However, present mobile communication networks do not support streaming for reasons described in the following.
The encapsulation of media content, message description and addressing information in a single entity as proposed in current MMS specifications is incompatible with the streaming of media content. In order to establish a streaming session, it is necessary for the receiving terminal to be aware, in advance, of certain information relating to the media content. Such information includes, but is not limited to, the type of media contained in the multimedia message, the way that media is encoded and a suitable transport protocol that can be used to download the media content. Because present MMS specifications require information describing the media content to be encapsulated with the multimedia message itself, the receiving terminal cannot obtain prior knowledge about the properties of the media content and therefore cannot establish any form of streaming session. Thus, according to the present MMS specification, the entire multimedia message must be downloaded to the receiving terminal in order for the details of the media content to be extracted. Only then can any media content, such as video and/or audio clips be played back to the user of the receiving terminal. This limits the usability of the present MMS because multimedia clips are usually bulky in terms of bits and therefore a receiving terminal, for example a mobile station, would require a comparatively large memory to completely receive the clips. The need to download an entire multimedia message before it can be presented may also give rise to significant delays in certain conditions, for example if the multimedia message is very large, or the data transmission rate of the connection is low.
It should further be emphasised that the addressing scheme suggested by current MMS specifications does not facilitate the implementation of streaming in such a system. The current MMS can be viewed as a “sender orientated” system. In other words, the sender decides what media content to send to the receiver, encapsulates that in the multimedia message and addresses the multimedia message to the intended receiver. Streaming, on the other hand, is more “receiver orientated”. To establish a streaming session, it is generally necessary for a streaming connection to be formed between the receiver and the sender, for example a network-based server, the content being streamed from the server once the necessary connection has been established. Thus, establishment of a streaming session requires the recipient to have knowledge of the location of the media content, but it does not necessarily require the media content to be directly addressed to the recipient.